Powder metallurgy is commonly used to produce high-volume components with good dimensional control. Typically, a powder metal and some amount of binder and/or lubricant are compacted in a tool and die set in order to form a “green” or un-sintered powder metal compact or preform. Such compacts or preforms are then heated to sintering temperatures just below the melting temperatures of the powder metal in order to cause the powder metal particles to sinter to one another. This sintering usually involves adjacent particles necking into one another to join or bond the powder metal particles to one another while, at the same time, reducing the porosity of the component and increasing its density. In some forms, the sintering step may include “liquid phase” sintering in which at least one of the powder metal constituents is engineered to melt into a liquid phase at sintering temperatures, thereby additionally providing liquid phase for transport at sintering temperatures. In any event, the sintering process forms a sintered powder metal component which is much stronger than the green compact or preform and which has exceptional dimensional accuracy as compared to parts made by other processes, such as for example, casting. In many instances, this sintered powder metal component is further processed by one or more of machining, forging, and so forth.
Although sintered powder metal components have their advantages, there are certain circumstances in which a single sintered powder metal component does not possess all of the desired properties for a particular application. In such circumstances, composite components are often used in which more than one material is used to produce the component. As one example, in order to form bi-material composite parts, pressing techniques have been developed in which multiple powder metals are filled into a single die and tool set (using complex dividers, for example) and then these materials are simultaneously compacted.
Nonetheless, known processes for production of composite components typically add severe complexity to existing process steps and/or add the need for additional fixtures to enable the formation of the composite. Further, even in the simplest case of diffusion bonding of two components, in which two components are placed adjacent to one another during the sintering step for at least one of the components, there are potentially concerns with consistent and accurate placement of the two constituent portions relative to one another as, if there is not a consistent interface quality between the portions, the sinter bonding may be relatively poor.
Thus, there exists a need for improvements in the field of powder metal composite component production.